In buildings such as laboratories, testing facilities and manufacturing plants in which explosions or other sources of high pressure build-up may occur, it is conventional to incorporate in the roof and/or walls of the buildings, panels that will blow-out to relieve over-pressures which may occur inside the building. This is necessary to prevent the building from collapsing and to minimize injury to persons inside the building.
Blow-out panels have in the past been retained by mechanical devices such as shear bolts which are designed to break under a predetermined load and allow the panel to blow-out. In this type of system it has been difficult to adjust accurately the pressure at which a particular panel will blow-out. In addition, as the system ages and corrodes, the pressure at which blow-out will occur tends to change. Further, when a panel has blown-out, part or all of the panel or at least the shear bolts are destroyed and must be replaced.
Accordingly, the assignee of the present invention, C/S Construction Specialties Limited of Mississauga, Ontario, Canada has developed a new pressure relief panel arrangement in which a calibrated magnet and striker set is used to hold the panel closed. The magnet has a maximum holding force substantially exceeding the known force to which it is subjected at the predetermined blow-open pressure, and at least one non-magnetic shim is used of thickness selected to reduce the magnet holding force to the known force. This system is described in Canadian patent 1,241,517 issued Sep. 6, 1988 entitled "PRESSURE RELIEF PANELS AND LOUVERS".
It has been discovered during tests of the system described in the above Canadian patent, that when an explosion occurs in a building protected by the panels, the panels blow open rapidly but may then tend to re-close quickly due to implosive forces which occur immediately after an explosion. Specifically, super heated gases which are created during an explosion rapidly cool and contract immediately after the explosion. This contraction causes an "implosive" or vacuum type condition which draws the panels closed. The resultant forces, if not addressed, are transferred to the building's structure and, depending on their magnitude, may cause considerable damage.
Therefore, it is an object of the invention to provide an arrangement and method in which, after a pivotally connected blow-open panel has been blown open at least to a predetermined extent, the panel is then held at least partly open to reduce the likelihood of implosion damage in the building being protected.